1. Field of the Invention
The present invention relates to a three-dimensional fabric suitable for use as a frame member of a composite that has an irregular, non-rectangular cross section, such as L shape, I shape, T shape or H shape, and a method of producing the same.
2. Description of the Related Art
Composite materials having three dimensional fabrics as their frame members are expected to be widely used as structural materials for various products including rockets, aircraft, automobiles, marine vessels and buildings. One common fabric structure is an orthogonal three-axis, three-dimensional fabric that includes three kinds of threads (X,Y and Z directional threads). Another is a five-axis three-dimensional fabric that includes oblique threads that extend in the lengthwise direction in addition to the perpendicular three axes. To ensure a variety of applications of a composite having a three-dimensional fabric as the frame member, it is sometimes necessary that the three-dimensional fabric have an irregular, non-rectangular cross section, such as L shape, I shape, T shape or H shape, depending on the actual usage.
A conventional three-dimensional fabric having an irregular cross section is disclosed in Japanese Unexamined Patent Publication No. 1-292162. This three-dimensional fabric includes at least two plates connected together by fabric threads. One or more of the plates includes threads that extend in three independent directions. Specifically, the longitudinal, lateral and transverse directions. This is referred to as a three-axis three dimensional fabric. At least one plate further includes two additional types of threads. That is, two types of oblique threads that extend in a direction oblique to the direction of the arrangement of the lengthwise and horizontal fabric threads and intersecting each other, thereby providing a five-axis fabric arrangement.
One such design is shown in FIG. 1. As seen therein, a three-dimensional fabric with an H-shaped cross section includes a first plate 31 as a base and four second plates 32 formed integrally and perpendicular to the plate 31. The plates 31 and 32 are linked by the transverse threads.
In producing this three-dimensional fabric, first thread guide pipes G1 and second thread guide pipes G2 are provided upright in a predetermined pattern. A layer consisting of fabric threads arranged in the X and Y directions is then laid on that portion of the bottom of the first plate 31 where the first guide pipes G1 are provided. Thereafter, a plurality of full fabric layers are woven through both sets of pipes G1 and G2. The full fabric layers include threads arranged in the X direction, Y direction and oblique directions. Subsequently, a layer consisting of threads extending in the X and Y directions is laid on top in the region of the first plate 31 where the first guide pipes G1 are provided. Next, fabric threads are inserted in the individual guide pipes G1 and G2 in a loop form so that they replace the guide pipes G1 and G2. A tack thread is inserted into each loop as a stopper. As a result, the individual layer portions are coupled by fabric threads extending in the Z direction, yielding a three-dimensional fabric with an H-shaped cross section.
The three-dimensional fabric does not have any threads which extend continuously through a bend into two perpendicularly-crossing planes. That is, none of the threads in the fabric shown in FIG. 1 which are arranged so as to be continuous to the X-Y plane and Y-Z plane. Therefore, when a stress is applied to the second plate 32 in the direction and location of arrow Q, the fabric threads in the X-Y plane of the first plate 31 carry very little of the bending stress acting on the second plate 32. In other words, the fabric threads of the X-Y plane of the first plate 31 do not effectively work to carry the loads applied to the second plate 32. Accordingly, composites using this three-dimensional fabric have the drawback of having insufficient strength.